Hydrogen is the environmentally desirable fuel of choice since it can be used in internal combustion engines or electrochemically oxidized efficiently in Proton Exchange Membrane (PEM), or other types of fuel cells.1 Presently, hydrogen storage processes are either inadequate or impractical for widespread use. The United States Department of Energy (DOE) has targeted a gravimetric density of 9% for on-board hydrogen storage for 2015.2 Higher hydrogen weight percentages are required for lightweight power supplies, particularly for the requirements of soldiers in the field.
Although many hydride complexes have been studied, amine boranes, particularly, ammonia borane (AB) (19.6 wt. % of H2), has unique potential to store and deliver a large amount of molecular hydrogen through dehydrogenation reaction. Accordingly, AB has been examined by several groups as a hydrogen source.3 Ammonia-borane, a white crystalline transportable solid of low specific weight, is stable in ambient air. Furthermore, the non-toxicity of AB makes it a superior carrier of hydrogen compared to ammonia.4 AB can liberate hydrogen through a stepwise sequence of reactions that occur at distinct temperature ranges. The byproducts of the reaction are ill-defined; depending on the conditions of dehydrogenation, monomeric BN heterocycles (e.g., cyclotriborazene, cyclopentaborazane, and borazine), polymeric amino- or iminoboranes, and/or polyborazylene materials have been reported.5 Liberation of the third equivalent of hydrogen from AB is not desirable, since the byproduct, boron nitride (BN), is isoelectronic to a similarly structured carbon lattice and has a melting point of 2973° C. The liberation of two equiv of hydrogen from AB provides polyborazylene (a polymer of borazine).5 However, trace amounts of borazine are also produced in this process. Hydrogen generated for fuel cell applications should be extremely pure and any traces of borazine will be detrimental to the fuel cell membrane. The removal of borazine has been a challenge for the application of AB in fuel cell cartridges. This led us to the examination of other amine boranes for hydrogen storage applications.
Methylamine borane complex (11.1% hydrogen), methylenediamine bisborane complex (13.5% hydrogen), and ethylenediamine bisborane complex (11.4% hydrogen) were considered for this application. Methylamine borane complex is known in the literature.6 Although methylenediamine bisborane complex is not known in the chemical literature, it can be prepared using the corresponding methylenediamine dihydrochloride7 and sodium borohydride. The low cost of ethylenediamine coupled with similar hydrogen storage capacity makes it an attractive reagent for synthesis of ethylenediamine bisborane (ethane 1,2-diaminoborane, EDAB)8 as a viable hydrogen storage material and contributor to the hydrogen economy.

Accordingly, there is a need in the art for economically efficient synthesis protocols for preparing EDAB, including corresponding synthesis reagents, such as AB.